This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2001-264357, filed Aug. 31, 2001; and No. 2001-280638, filed Sep. 14, 2001, the entire contents of both of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a magnetic head measuring apparatus for measuring a magnetic head.
2. Description of the Related Art
A magnetic force microscope (MFM) is often used in inspecting a magnetic head. For example, the following inspection method used in a thin-film magnetic head wafer inspection process is known. That is, with a plurality of thin-film magnetic heads formed on a wafer, a groove is formed in a surface on which a medium and the head gap of each thin-film magnetic head are in contact with each other. A probe of the MFM is inserted into this groove to inspect the shape of the head gap surface and the electromagnetic conversion characteristic of the thin-film magnetic head.
The MFM is a kind of a scanning probe microscope (SPM), and is an apparatus which detects a dynamic interaction between a pointed probe (MFM probe) which is a magnetic material, or a nonmagnetic material to which a magnetic material is adhered, and a magnetic field generated from a sample to be measured. The resolution is as very high as several tens of nm, although it depends upon the measurement method and the probe shape. Therefore, this MFM is very effective in magnetic characteristic evaluation on submicron order.
The MFM probe is supported by a leaf spring called a cantilever and has a mechanical resonance frequency determined by the mass of the MFM probe and the sprint constant of the cantilever. Accordingly, in MFM measurements in a normal mode, responses at frequencies higher than this mechanical resonance frequency (generally a few tens of kHz to a few hundred kHz) cannot be measured in the case where the response is measured by applying sinusoidal wave.
In the above inspection method, the MFM measurement is performed while applying a sinusoidal high-frequency electric current to the recording head. However, no desired response can be obtained from the measured MFM signal owing to the above limitation; a high-frequency component is contained in a DC signal. Also, the DC component of the measured MFM signal contains contribution from factors other than the head, e.g., an MFM interaction caused by a DC magnetic field generated from the head magnetic pole. Under the measurement conditions like this, the distribution of a true magnetic field generated from the magnetic head cannot be measured. In other words, strict magnetic head inspection is difficult to perform.
Furthermore, in MFM measurements, measurement values vary owing to tip variations when the MFM probes are changed (in some cases measurement values vary even for the same magnetic head as a sample to be measured). One reason is that the conditions (e.g., the shape, film thickness, and contamination) of a magnetic material at the tip of the MFM probe more or less change from one probe to another. Other reasons are variations in an optical system alignment for measuring the deflection of the cantilever supporting the MFM probe, and detection sensitivity variations caused by a difference in reflectance between thin metal films adhered to the back surface of the cantilever and required in the optical system alignment.
When the foregoing facts are taken into consideration, it is necessary to compensate for the influence of tip variations in the process of inspecting a large amount of magnetic heads. However, the above-mentioned references do not describe any method of solving this problem.
As described above, the conventional methods have the problems that no true high-frequency magnetic field can be measured, and the obtained measurement data have measurement variations caused by tip variations.
Also, electromagnetic conversion measurement for a magnetic head is conventionally performed using, e.g., a spin stand. This measurement must be performed with a magnetic head in the form of HGA (Head Gimbals Assembly). That is, since magnetic heads including defective ones are measured in the form of HGA, the yield cannot be improved unlimitedly.
From the foregoing, the presentation of a magnetic head inspection technology that can reduce measurement variations caused by tip variations and which can improve the yield is desired.
In the meantime, a magnetic recording-head as a sample to be measured by a magnetic head measuring device is, e.g., an inductive type thin-film head and has a magnetic gap that generates a recording magnetic field corresponding to a signal current applied to a coil. The magnetic head measuring device applies a high-frequency signal current to (the coil) of a head as a sample, and measures the distribution of a magnetic field generated from the magnetic gap. One practical measurement method is to detect the phase or deflection (dynamic interaction resulting from a head magnetic field) of a cantilever vibrating and, on the basis of this detection result, measure the force gradient or force acting between the probe and the sample. In this method, measurement is performed using the relationship that the phase of the cantilever approximates the force gradient and the deflection of the cantilever approximates the force.
This measurement method has wide variations. For example, R. Proksch et al., xe2x80x9cMeasuring the gigahertz response of recording heads with the magnetic force microscopexe2x80x9d, (Digital Instruments et al.), Applied Physics Letters, Vol. 74, No. 9, March 1999, pp. 1308-1310 (to be referred to as prior art 1 hereinafter) discloses a technique which applies an amplitude-modulated electric current to a magnetic recording-head and matches the modulation frequency to the resonance frequency of the cantilever, thereby detecting the resonance frequency component of the deflection (or force) of the cantilever vibrating. This technique improves the sensitivity by using the Q value of the mechanical resonance frequency of the cantilever.
Also, Hiroyuki Ohmori, xe2x80x9cTechniques of Evaluating and Analyzing Recording and Reproduction Headsxe2x80x9d, SONY CORP., Journal of Japan Applied Magnetics Society, Vol. 23, No. 12, 1999, pp. 2111-2117 (to be referred to as prior art 2 hereinafter) discloses a technique which applies a high-frequency sinusoidal wave to a magnetic recording-head and measures the DC component of the phase change (force gradient) of the cantilever, resulting from a magnetic field generated around the head.
In prior art 1, however, the deflection of the cantilever is detected as magnetic field strength. Therefore, the vibration amplitude of the cantilever is not constant during probe scanning. In the case of the measurement which detects dynamic deflection of the cantilever such as the measurement in prior art 1, detected interaction on the probe depends on the cantilever amplitude, probe-sample distance, magnetic field and so on. Therefore, cantilever amplitude and probe-sample distance need to be constant during probe scanning, since magnetic field decays non-linearly. So an image reflecting a magnetic field cannot be measured. In addition, the sensitivity is improved by using the Q value of the mechanical resonance frequency of the cantilever. However, a high Q value may produce a response delay in a change of the cantilever.
On the other hand, prior art 2 measures the DC component of the phase change (force gradient) of the cantilever, resulting from a magnetic field generated around a head. However, this DC component contains contributions other than the high-frequency component, so the obtained data is difficult to analyze.
In either method, the frequency of a magnetic field generated from a magnetic recording-head is on the MHz order, i.e., much higher than the cantilever mechanical resonance frequency which determines the response speed of the scanning probe microscope. This makes it difficult to extract only a high-frequency response and measure this response at high sensitivity and high resolution.
From the foregoing, the presentation of a magnetic recording-head measurement technique capable of measuring a high-speed response at high sensitivity and high resolution is desired.
Accordingly, it is an object of the present invention to provide a magnetic head measuring apparatus capable of measuring a high-speed response at high sensitivity and high resolution, and a magnetic head measuring method.
According to one aspect of the present invention, there is provided a magnetic head measuring apparatus for measuring a magnetic head, comprising a calibrating magnetic field generating source which causes the magnetic head to generate a magnetic field having a constant strength and frequency; an electric current applying device which applies an amplitude-modulated electric current whose amplitude is modulated by a specified carrier wave frequency and modulation frequency, to the magnetic head from which the magnetic field is generated by the calibrating magnetic field generating source; and a magnetic head measuring device which measures a high-frequency magnetic field generated from the magnetic head by application of the amplitude-modulated electric current from the electric current applying device.
According to another aspect of the present invention, there is provided a method of inspecting a magnetic head, comprising setting the magnetic head; selecting an analysis item for which the magnetic head is to be inspected; applying to the magnetic head an amplitude-modulated electric current whose amplitude is modulated by a specified carrier wave frequency and modulation frequency; measuring, in accordance with the selected analysis item, the magnetic head to which the amplitude-modulated electric current is applied, by using a high-frequency magnetic force microscope; analyzing and evaluating data, obtained by the measurement, of the magnetic head; and determining success or failure of the magnetic head on the basis of the evaluation result.
According to still another aspect of the present invention, there is provided a magnetic recording-head measuring apparatus for measuring a magnetic recording-head, comprising an electric current applying device which applies to the magnetic recording-head an amplitude-modulated electric current whose amplitude is modulated by a specified carrier wave frequency and modulation frequency; a cantilever to which a probe having a magnetic material is attached; a vibrator which applies a vibration with specified vibration amplitude to the cantilever; and a measuring device which measures a dynamic interaction which a magnetic field generated in the magnetic recording-head by application of the amplitude-modulated electric current from the electric current applying means exerts on the probe vibrating, wherein while the probe is scanned to measure the dynamic interaction by the magnetic field, a vibration range of the probe falls within a range from a surface of the magnetic recording-head to a point at which the probe does not interact with the magnetic field any longer.
According to still another aspect of the present invention, there is provided a method of measuring a magnetic recording-head, comprising applying to the magnetic recording-head an amplitude-modulated electric current whose amplitude is modulated by a specified carrier wave frequency and modulation frequency; applying a vibration with specified vibration amplitude to a cantilever to which a probe having a magnetic material is attached; and measuring a dynamic interaction which a magnetic field generated in the magnetic recording-head by application of the amplitude-modulated electric current exerts on the probe which vibrates together with the cantilever, wherein while the probe is scanned to measure the dynamic interaction by the magnetic field, a vibration range of the probe falls within a range from a surface of the magnetic recording-head to a point at which the probe does not interact with the magnetic field any longer.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.